Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$130.88	6.467%	$139.344	$139.34	$139.35	$139.30
Purchase #2	$228.88	4.657%	$239.5389	$239.54	$239.55	$239.50
Purchase #3	$68.85	13.512%	$78.153	$78.15	$78.15	$78.20
Purchase #4	$221.53	6.173%	$235.205	$235.21	$235.20	$235.20
Purchase #5	$72.84	7.446%	$78.2637	$78.26	$78.25	$78.30
Purchase #6	$202.93	11.309%	$225.8794	$225.88	$225.90	$225.90
Purchase #7	$250.68	3.125%	$258.5138	$258.51	$258.50	$258.50
7 purchase totals =	$1,176.59		$1,254.8978	$1,254.89	$1,254.90	$1,254.90